Collect, Organize, and Analyze We need to write a balanced chemical equation for the combustion of C_{2}H_{6}. The products of complete combustion of hydrocarbons are carbon dioxide and water.

Solve The preliminary expression with single particles of all known reactants and products describing the combustion of ethane is

C_{2}H_{6}(g)+O_{2}(g)\rightarrow CO_{2}(g)+H_{2}O(g)

Because this reaction is between oxygen and a hydrocarbon, we balance C first, then H, then O. Balance the carbon atoms first by giving CO_{2} in the product a coefficient of 2:

_ C_{2}H_{6}(g)+ _O_{2}(g)\rightarrow \underline{2} CO_{2}(g)+ _ H_{2}O(g)

Then balance the hydrogen atoms by giving H_{2}O a coefficient of 3:

_ C_{2}H_{6}(g)+ _O_{2}(g)\rightarrow \underline{2} CO_{2}(g)+\underline{3} H_{2}O(g)

At this stage, the oxygen atoms cannot be balanced with a simple whole-number coefficient for O_{2}; we need \frac{7}{2}O_{2}. However, if we give O_{2} a coefficient of 7 and double the coefficients for ethane, carbon dioxide, and water, we can write

\underline{2}C_{2}H_{6}(g)+ \underline{7}O_{2}(g)\rightarrow \underline{4} CO_{2}(g)+\underline{6} H_{2}O(g)

This equation is balanced.

Think About It Balancing chemical equations for combustion reactions of hydrocarbons often requires several iterations of the coefficients before all of the elements are balanced.